(i) Field of the Invention
The present invention relates to a method for increasing the storage carbohydrate content of sugarcane plants.
(ii) Description of the Related Art
Those involved in the fields of agriculture and forestry constantly strive to provide higher-yielding plants, in particular to safeguard the food supply of the continuously increasing world population and to ensure the supply of renewable raw materials. A traditional attempt is to maintain high-yielding plants by means of breeding. However, this procedure is time- and labor-consuming. In some cases, progress has already been made by subjecting plants to genetic manipulation, i.e. by the directed introduction and expression of foreign (recombinant) nucleic acid molecules in/into plants.
Besides sugar beet, sugarcane is the most important plant used for the production of sugar (sucrose). To obtain cane sugar, the sugarcane is harvested in an expensive fabrication procedure and then transported to the factory. Prior to the extraction of the sugar, the sugarcane is cleaned. In the traditional method, the sugarcane is subsequently comminuted and then passes through 4-6 roller presses to separate the juice from the fiber (bagasse). The crystallized and centrifuged sugar (sucrose) is obtained by clarification, evaporation, fractional crystallization and separating the mother liquor (molasses) from the crystals by centrifugation. The molasses, is currently the economically most important by-product of obtaining sugar from sugarcane, comprise approximately 50% sugars (sucrose and monosaccharides). They is used as starting material for fermentation products, of which ethanol is the most important, and moreover as animal feed and, in some countries, also for human nutrition (“black honey” in Egypt).
Current biotechnological methods allow the generation of sugarcane plants which, besides cane sugar (sucrose) and molasses, synthesize valuable storage carbohydrates such as, for example, fructans, which can subsequently be employed for industrial, cosmetic or pharmaceutical purposes and in the food industry.
Thus, for example, the international patent applications WO96/01904, WO96/21023, WO98/39460 and WO99/24593 propose to express 1-SST genes alone or in combination with 1-FFT genes in sugarcane in order to produce fructans in transgenic sugarcane.
Obtaining storage carbohydrates (sucrose and fructans) from sugarcane plants in an efficient manner requires methods which lead to increasing the storage carbohydrate content in sugarcane plants.